The present invention is directed to an eye chart with distinct symbols. In particular, the eye chart has lines of symbols, where the symbols are selected from a set of distinct symbols. The symbols include at least one of letters, numerals and pictorial objects. In one embodiment, a first subset of symbols has a first color and a second subset has a second color. The eye chart permits consistent quantification of visual acuity, which aids in testing, diagnosing, and monitoring of neurological and ophthalmological diseases, loss of color vision, and retinal dystrophies, as well as monitoring of effectiveness and dosage of some drugs.
A Snellen test is typically used to determine visual acuity. The Snellen test has a patient identify black block letters of the alphabet from an eye chart at a specified distance away from a Snellen chart. Typically, a doctor records the value associated with the line on the Snellen chart that the patient reads completely, e.g., 20/20. If the patient misses some letters on the 20/20 line, the doctor would write down xe2x80x9c20/20xe2x88x92xe2x80x9d for 20/20 minus. Some doctors use a Jaeger card to test a patient""s visual acuity. The values of visual acuity for Jaeger are noted as, for example, J2, J4, and J6.
Snellen devised the familiar eye chart by defining a person with normal visual acuity as having a threshold visual angle of 1 minute of arc for black objects on a white background. One with normal visual acuity has 20/20 (6/6) vision. 20/20 (6/6) vision means the person has read a letter at 20 feet (6 meters) that was designed to be read at 20 feet (6 meters).
Accuracy of identification of the letters in the Snellen chart is based upon experience of the user with the chart and in reading the letters, familiarity with the letters, and psychological factors. Further, accuracy depends upon whether the chart letters are equally legible or whether some blur interpretation may be characteristic of the configuration of some of the letters. For example, as compared with the letter C, G is more difficult to identify and L is easier to identify.
Typically, the details of the symbols blur as the distance from the eye increases (or as the font decreases) and identification becomes more difficult. Some clinicians recognize that some symbols are similarly formed and, at a distance, look strikingly similar. As a result, the clinicians will sometimes credit the person taking the vision test with accurately identifying the strikingly similar symbol, and other times clinicians only give credit for identifying the exact symbol accurately. This type of subjective judgment leads to inconsistent quantification of vision acuity.
Visual acuity testing for illiterate persons, including children, typically utilizes designated illiterate charts having lines with symbols. These charts typically have symbols of a xe2x80x9cTumblingxe2x80x9d E, wherein the person identifies with fingers the direction of the E. Other charts used to test visual acuity for illiterates include pictorial objects that are identified, and an HOTV chart for an HOTV test. In the HOTV test, the person matches each test letter to one of the four letters H, O, T, or V printed on a card that can be held in the person""s hands.
Typically, a patient is tested for color blindness using Ishihara plates. Ishihara plates have colored dotted symbols on a colored dotted background. Typically, the red-green pattern of loss is most common.
Lesions of the inferior occipital cortex, neurological diseases, strokes, Multiple Sclerosis, and other disorders typically affect and disrupt color perception. The disruption in color perception results in reduced vividness of saturated or pure colors, particularly red. Testing of red desaturation is most often performed clinically by estimating the degree of desaturation by having the patient view a red object such as the red cap of a bottle of eye drops.
An eye chart of the present invention has a plurality of lines, each line with a plurality of symbols chosen from a set of symbols. The symbols in the set include letters and numerals, wherein each symbol in the set is substantially equal in size and distinguishing features. In one embodiment, the symbols in the set further include a pictorial object. The pictorial objects have non-confusing, distinct shapes.
A method for vision testing of the present invention includes recording values associated with an accuracy of identification of a letter and of a numeral on an eye chart by a patient, and comparing the two values for each eye of the patient. In one embodiment, the method further records a value associated with an accuracy of identification of the pictorial object on the eye chart, and compares the value associated with the accuracy of identification of the pictorial object with that of the letter and numeral.
In another embodiment, the method further records a value associated with an accuracy of identification of a first and a second set of symbols on the eye chart, and compares the two values. The first set of symbols is in a first color and the second set of symbols is in a second color. In one embodiment, the chart enables evaluation of subtle loss of color perception and the change over time.
In one embodiment, the numerals in the set of symbols consist of 3, 4, 6, 7, and 9. In another embodiment, the letters in the set of symbols consist of A, E, F, H, J, K, L, P, T, X, and Y. Letters and numbers that tend to be confused with each other are excluded. The letters may also be distinct characters of an alphabet other than the Latin alphabet. In one embodiment, at least one of the symbols is black, and at least another of the symbols is one of red and green.
Because of the distinct symbols, the eye chart permits doctors to render substantially consistent quantification of neurological abilities and changes therein. The methods of quantification of visual acuity permits testing or monitoring of loss of color vision, neurological diseases, drug treatments or retinal dystrophies by comparing the visual acuity for colored symbols to that of black symbols. Further, by comparing the visual acuity for letters and numerals, neurological diseases may be diagnosed and monitored.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts throughout.